This project is concerned with studies of the genetic diversity of Trypanosoma cruzi and the implications of this diversity in the presentation and course of Chagas' disease. Emphasis has been placed recently on the consolidation, correlation and extension of studies of about 50 T. cruzi clones derived from various sources. The T. cruzi clones can be divided into 13 distinct subpopulations on the basis of restriction endonuclease (EcoRI) digests of their kinetoplast DNA. Some of the T. cruzi clones derived from isolates maintained in the laboratory for long periods of time prior to cloning (e.g. Y strain) have identical EcoRI digest profiles. However, one of five clones of Tulahuen strain (maintained in continuous passage for over 30 years prior to cloning) still demonstrates a restriction endonuclease profile that is different from the other four. A correlation was established between EcoRI digest profiles and total DNA/organism as determined by flow cytometry. Flow cytometry studies of total DNA/organism were extended to include analyses with propidium iodide. Results were identical to those obtained with mithramycin indicating that the difference in total DNA/organism between clones is not due to differences in G-C content alone. Metabolic labeling (35S-methionine) and cell surface protein labeling (125I-Iodogen) of selected clones demonstrate the existence of marked genotypic and phenotypic differences. The phenotypic differences can be correlated to differences in immunochemical reactivity through the use of monoclonal antibody reactivity (or lack of reactivity) of the various clones. The intracellular growth rates of amastigotes correlate to the extracellular rate of growth of epimastigotes in LIT medium. Consequently, the diversity in LIT growth rates of the clones is not due to "nutritional mutants" or culture system deficiencies. The growth of epimastigotes in LIT medium can be correlated to the sensitivity or resistance of the organisms to allopurinol and/or allopurinol ribonucleoside-5' monoshosphate (compounds that are being considered for clinical trials in the treatment of Chagas' disease).